Osteoarthritis is caused by cartilage in a person's knees breaking down over time due to age, accumulated physical strain, etc. The loss of cushioning cartilage in the joint allows bone-on-bone contact, leading to chronic pain. Often, the afflicted knee joint is highly swollen and enlarged. One popular treatment is having the osteoarthritis sufferer wear a knee brace to reduce the knee joint pain and to provide him or her with mobility.